A touch display device and an improvement method to a touch display device are disclosed. The improvement method first determines whether the touch display device turns on the touch mode. If yes, image data input to the touch display device is obtained and feature data is extracted from the image data. Then, adjustment or compensation factors are obtained according to the feature data. Grey level compensation sequence is also obtained. The duty cycle of the control signal for the touch display device is adjusted according to the factors and the grey level compensation sequence, so as to improve the display difference for a same grey level image due to the turning on of the touch mode.